Television cameras, camcorders, and other such imaging devices are equipped with an optical system having a zoom function, and a lens barrel that supports this optical system. The optical system has a plurality of lens groups. The lens barrel has a barrel main body and a lens movement frame that supports the lens groups. The lens movement frame is provided movably with respect to the barrel main body. The focal distance of the optical system can be varied by moving the lens movement frame in the optical axis direction with respect to the barrel main body.
A cam barrel is used to move the lens movement frame in the optical axis direction. The cam barrel is provided rotatably with respect to the barrel main body, and has a spiral guide groove that guides the lens movement frame. The lens movement frame has a linking pin that is inserted in the guide groove. When the cam barrel is rotated and driven with respect to the barrel main body, the linking pin is guided by the guide groove, and the lens movement frame moves in the optical axis direction with respect to the barrel main body according to the shape of the guide groove.
With a lens barrel such as this, known techniques for detecting the position of the lens movement frame include those discussed in Patent Citations 1 and 2, for example.
With the lens barrel discussed in Patent Citation 1, a pattern plate is provided as a detected member to the inner peripheral wall, and a photoreflector is provided as a detecting sensor so as to be opposite the pattern plate. The pattern plate and the photoreflector are used to detect the position of the cam barrel in the rotation direction, which allows the position of the lens movement frame to be calculated with respect to the barrel main body.
The lens barrel discussed in Patent Citation 2 has a first lens movement frame, a cam barrel with a groove for guiding the first lens movement frame, and a second lens fixing frame that is fixed to the barrel main body. A comb-like member is provided as a detected member to the first lens movement frame. A photointerruptor is provided as a detecting sensor to the second lens fixing frame. The pattern plate and the photointerruptor can be used to calculate the position of the first lens movement frame with respect to the second lens fixing frame.
Patent Citation 1: Japanese Laid-Open Patent Application 2004-184734
Patent Citation 2: Japanese Laid-Open Patent Application 2006-243668